Aircraft are often provided with tanks in the main fuselage of the aircraft for holding various liquids, such as fuel or water. These tanks may be used to extend the range of the aircraft, for mid-air fueling of other aircraft, for transporting supplies to land operations, or other activities. Mounting such a tank in a body assembly, that is, a section of the fuselage, involves sliding the tank into place so that holes in mounting lugs on the tanks are placed over pins coupled to mounts of the body assembly. The tanks generally match the outline of the body so that there are often only a few inches or less of gap between the body assembly and the tank. Because of this, the far end of the tank and the far end mounts with their associated pins are not accessible after the tank is place.
The tank should be properly located with respect to the mounts, that is, that the tank lugs are preferably located within a narrow range of acceptable distances from the mounts brackets on their respective pins. However, because the far end, or distal end, pins and lugs are blocked by the tank itself, this critical distance cannot be measured directly by manufacturing personnel at the time of installation or verified by inspectors.
A prior art method of ensuring that the distal end lugs are properly located on their respective pins involves measuring a mounting gap on the proximal end of the fuel tank, using a specially manufactured caliper to measure a distance to the distal end lug, measuring a distance between body-assembly mounts, and mathematically calculating the mounting gap on the distal end. This process is time consuming and is susceptible to both measurement errors and calculation errors.